In various circuit applications where the control of current to a load connected across the DC voltage source is to be maintained, it is often desirable to connect a high current switching transistor is series with the load to achieve control of current therethrough. Applying a voltage of sufficient magnitude to the base of the high current transistor causes the high current transistor to be conductive and permits a current to flow between the collector and emitter terminals, thereby permitting current to flow through the load. Control of the load voltage and current through the load is achieved by control of the switching of the high current transistor.
In circuits operated in this manner, usually a single, relatively high, DC potential source is available. It is, therefore, necessary to provide some means to reduce this potential so that an appropriate value of DC potential may be applied across the base-emitter junction of the high current transistor.
In the past, apparatus such as DC-DC converters or voltage dividers have been employed to provide appropriate base voltage to control the high current transistor. In one such circuit according to the prior art of which the inventors are aware, a voltage divider network comprised of a resistor and a control transistor in series is connected across a DC voltage source with the base of the high current transistor connected to the junction of the resistor and the collector of the control transistor. Typically, the load in this prior art circuit is serially connected with the collector of the high current transistor across the DC source and is controlled by causing the control transistor to alternate between a nonconductive and a conductive condition. When the control transistor is forced into being conductive, current will flow through the resistor and the collector electrode of the control transistor. With current flow through the collector of the control transistor, the corresponding base-emitter potential of the high current transistor will be relatively low, causing the high current transistor to be nonconductive and thus causing the load to remain de-energized
When the control transistor is nonconductive, the base-emitter potential developed across the high current transistor will be high, rendering the transistor conductive and thus permitting load current to flow through the collector electrode. A major disadvantage in such a circuit is that current continuously flows in resistor 110. This results in substantial undesirable power losses.